This grant application focuses on developing a new approach for preventing occupational asthma caused by isocyanates, the essential cross-linking chemical for making polyurethane. Despite recognition of isocyanate's allergenicity for over 60 years, these chemicals remain a leading cause of asthma world-wide. Disease prevention efforts focus primarily on exposure reduction, as exposure is the best-recognized risk factor for development of pathogenic chemical hypersensitivity. However, methods of exposure surveillance / monitoring, essential to guiding effective industrial hygiene and identification of exposure risks, are limited. We propose that a signature peptide method can be developed for bio-monitoring isocyanate exposure, by quantitating the amount of a specific chemical-peptide conjugate that results from exposure. We predict the level of chemical conjugate that accumulates and circulates in the peripheral blood, albeit low on an absolute scale, are proportion to the internal does received and thus, represent an effective biomarker for exposure surveillance. If these initial hypotheses are proven through the experimental data generated through the presently proposed studies, the signature peptide methodology may ultimately be employed as an effective approach to isocyanate asthma prevention. Furthermore, the study may serve as a model for other occupational / environmental exposures to reactive low-molecular weight chemicals. The approach of the present study involves using selected reaction monitoring-mass spectrometry of serum samples spiked with a heavy isotope labeled peptide conjugated to chemical. The sensitivity of the approach will be increased further; by using novel anti-MDI monoclonal antibodies to immunoaffinity purify the signature peptide before analysis. The specific aims of the project are- Aim 1. Develop quantitative assay for measuring MDI-peptide purified from human serum samples by affinity chromatography, followed by LC-MS/MS. Aim 2. Quantitate the amount of signature MDI-peptide present in serum of workers with varying levels of MDI exposure. Aim 3. Determine the association between signature MDI-peptide and personal exposure levels, estimated from task-based exposure measurements, urine analysis and occupational history. NORA Sectors & NIOSH r2p Output/Outcomes- The present application addresses the following NORA sectors and cosectors, in the following order of relevance; Exposure Assessment, Manufacturing, Construction, Immune and Dermal Diseases, and Respiratory Diseases.